The present invention relates to the field of semiconductor devices. More specifically, the present invention relates to an apparatus and method for eliminating substrate contamination defects in semiconductor devices.
High activation energy deep ultraviolet photoresists have high etch selectivity and low proximity bias. In addition, high activation energy deep ultraviolet photoresists have low degassing and long shelf life. The high etch selectivity and low proximity bias of high activation energy deep ultraviolet photoresists makes them particularly desirable for patterning small dense structures such as the metal local-interconnect layer, which can have a minimum dimension similar to that of poly-gate structures.
However, high activation energy deep ultraviolet photoresists have poor environmental stability. More particularly, deprotecton of high activation energy deep ultraviolet photoresists occurs at the post-exposure bake step. Because there is a time gap between exposure and the post-exposure bake step, airborne base and basic substrate species enter into the photoresist film. These substrate species neutralize acid and stop deprotection. This results in substrate contamination defects in the photoresist film.
In one prior art photolithographic processes, an anti-reflective coating is used in conjunction with an overlying silicon dioxide barrier layer. The silicon dioxide barrier layer is effective for reducing photoresist footing and scumming. However, the silicon dioxide barrier layer does not eliminate footing and scumming. In addition, the silicon dioxide barrier layer is not effective for preventing all substrate contamination defects, such as localized resist swelling defects.
Swelling defects are areas within the photoresist film where features have xe2x80x9cswelled,xe2x80x9d or uniformly increased in size. Footing and scumming defects tend to occur in a widespread fashion across the entire substrate. However, swelling defects are highly localized substrate contamination defects that typically occur over contact plugs. For example, when high activation energy photoresist is used to pattern a metal local-interconnect layer, swelling defects commonly occur where the photoresist overlies an interconnect. This swelling can cause bridging of adjacent photoresist features. This can result in bridging of features in the metal local-interconnect layer, resulting in reduced yield and increased manufacturing cost.
Thus, there is a need for a photoresist structure and a method for forming a photoresist structure that does not have swelling defects. In addition, there is a need for a patterned metal layer and a method for forming a patterned metal layer that does not have swelling defects. In addition, there is a need for a method and apparatus that meets the above needs and that reduces footing-related defects and scumming-related defects. The present invention meets the above needs.
The present invention provides a photoresist structure and a method for forming a photoresist structure that does not have swelling defects. In addition, the present invention provides a patterned metal layer and a method for forming a patterned metal layer that does not have swelling defects. Also, the method and apparatus of the present invention reduces footing-related defects and scumming-related defects. By eliminating swelling defects and reducing footing-related defects and scumming-related defects, manufacturing yield is improved and manufacturing costs are reduced.
A method for forming a photoresist structure on a semiconductor substrate is disclosed. A layer of low activation energy photoresist is disposed over a substrate that is to be patterned. A layer of high activation energy photoresist is then deposited such that the layer of high activation energy photoresist directly overlies the layer of low activation energy photoresist.
An exposure step is performed, followed by a heating step (post-exposure bake) and a developing step. The low activation energy photoresist acts as a substrate contamination barrier, protecting the overlying high activation energy photoresist layer. This results in a photoresist structure that does not have swelling defects where the photoresist structure overlies interconnects. In addition, the photoresist structure has reduced footing and scumming.
Because the photoresist structure does not have swelling defects, the subsequent etch step results in a patterned substrate that does not have swelling defects. In addition, the patterned substrate has reduced footing-related defects and reduced scumming-related defects. Accordingly, manufacturing yield is improved and manufacturing costs are reduced.
These and other advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments, which are illustrated in the various drawing figures.